Specification work is ongoing by the Third Generation Partnership Project (3GPP) for home base stations in Wideband CDMA/Universal Terrestrial Radio Access Networks (WCDMA/UTRAN) and in E-UTRAN (Evolved UTRAN), which is the next generation of Radio Access Network (RAN). These specifications contemplate using a UTRAN base station to provide home or small area coverage for a limited number of users. The Home Node B (HNB) would provide normal coverage for its end users and would be connected to a mobile core network via a Home NodeB Gateway (HNB GW) using some kind of IP based transmission. The coverage provided by such an arrangement is called femtocell in this document.
One of the main drivers of this new concept of providing Local Access is to provide cheaper call or transaction rates/charges when connected via the HNB, as compared to when connected via the Node B—i.e., it may be cheaper to connect to a wireless communication service provider's core network using an IP-based link provided by a local access point, than to connect through a wide-coverage base station in the provider's cellular network.
The HNB would, in most cases, use the end user's already existing broadband connection (e.g. xDSL, Cable) to achieve connectivity to the mobile operator's HNB Gateway (HNB GW). Over the broadband connection and other possible intermediate IP networks (e.g. the internet), a HNB communicates with the HNB GW in the operator's network via an IPsec tunnel (Internet Protocol security architecture according to RFC 4301). The IPsec tunnel, which is established between the HNB and a Security Gateway (SEGW), protects the border of the operator's network and the communication between the HNB and the HNB GW.
Further, the E-UTRAN standards for 3GPP Release-8 introduce the concept of Closed Subscriber Groups, referred to as CSGs. Later releases of the UTRAN standards also may adopt the CSG concept. Also several 3GPP working groups are currently conducting research and discussions on approaches that can be adopted for access controls of CSGs. In any case, with CSG, particular HNBs can be associated with certain mobile terminals, or other user equipment (UE), meaning that only the associated terminals are allowed to access the HNB(s). The allowed CSGs are stored in a given terminal, in a so called CSG Whitelist (that is also known as Allowed CSG List). Each HNB broadcasts a “CSG Indicator” and the CSG Identity allocated to it in System Information (SI). Thus, a terminal that “hears” a CSG being broadcast by a given HNB can determine whether the broadcasted CSG identity matches a CSG identity in the CSG Whitelist stored in the terminal. If so, the terminal knows that it is allowed to access that HNB.
The 3GPP requirements are that the “owner” of the HNB (or, equivalently, a Home eNodeB, HeNB) shall, under network operator supervision, be able to add, remove and view the list of CSG members. Because of this CSG-based access control arrangement, additional authorization control shall be performed in the operator's Core Network (CN). That is, for CSG terminals, the CN can check the CSG ID with UE Identity, to decide whether a given UE (terminal) should or should not be allowed access to a particular CSG.
However, a major difference in CSGs between the E-UTRAN and UTRAN standards relates to “legacy” issues. Because 3GPP Release-8 is the first release for E-UTRAN and it includes CSG support from the outset, there will be no legacy E-UTRAN UEs that do not support CSG. The case is different, however, for UTRAN, as previous releases of the UTRAN standard did not support CSG (e.g., Release-99). As such, UTRAN/3G HNB solutions will need to work with UEs that support CSG, and with those that do not.
The standardization work in 3GPP for UTRAN/3G HNB solutions is currently two-fold. The 3GPP TSG RAN3 is working with a solution that will support legacy UEs. In addition, it is also assumed that solutions supporting CSG-capable UEs will be standardized, either in Release-8 and/or in Release-9. Particularly, in UTRAN HNB standardization it has been agreed to introduce a UE registration procedure to support the access control in HNB GW for legacy terminals, i.e. terminals that do not support the CSG concept.